The efficiency of semiconductor light emitting diodes (LEDs) is improving rapidly and has become the ideal source for efficient displays that are capable of outdoor, public buildings or sport arenas viewing under relatively high ambient light. For example, gallium nitride (GaN) LEDs have improved to the capability of emitting up to 150 lm/W. But a GaN wafer to build LED display is too expensive because the cost per unit area is too high. On the other hand, the brightness of a GaN LED can be driven to a level that is more than 103-104 times the needed brightness for outdoor display board or indoor TV screen. One idea is to use small GaN LED chips as the light generating elements and to place small chips on a large pitch to create a large size display with thin thickness profile. Further, by using smaller chips, the cost of the display is substantially lowered. The dilution factor (area of a pixel/area of GaN LED chip) can be larger than 1000 even for outdoor viewing purposes. This is possible because, with proper design and process, GaN LEDs can be made efficient even for die as small as 10 μm.
There have been large size display boards constructed with LED tiles/modules. Each LED tile/module comprises LED elements typically in format of 8×8, 16×16, 32×32. The LED elements on each tile are connected in so-called passive matrix array form with each LED mounted at the cross-point of each row and column electrode bus line. A large-size display board is formed with typically 102-103 pieces of such tiles. One limiting factor of such display is the cost per area due to related driving circuit and components used. Another limiting cost factor is related with the conventional picking and place manufacture method of placing the LED (typically in surface mounting package) on the tile substrate (typically a printed circuit board, PCB). Because of these limiting factors, such displays have only been used in public areas (such as sport arena or outer wall of commercial buildings in central cities) for advertisement purpose.
However, one major problem in such display board is its related poor uniformity. This is due to the human eye can detect a small difference in brightness or colorimeter between adjacent or neighboring pixels. A substantial difference in brightness and color of emitted light can exist between chips selected from different areas of a common chip or from different chips. This effect can be easily seen in current LED display boards compiled with passive matrix LED tiles, especially in images with multiple gray levels. The LED display elements in a given passive matrix tile, and among different tiles were assembled without preserving neighborhood relationship on the original wafer. Therefore, it is important to preserve the relative positions of the chips as they were positioned on the wafer when originally manufactured, i.e. the preservation of a “neighboring relationship”. Also, using standard pick-and-place methods and apparatus, LED chips are transferred from a wafer to a substrate one chip at a time. Thus, transferring large numbers of chips (e.g. 1000×1000) onto a display substrate requires 1 million steps. This process is extremely time consuming and costly with existing picking and placing process tools. A state-of-the-art automatic picking-and-placing tool can transfer 103-104 chips per hour. The smallest chip size in surface mounting package is 100 um×100 um, within surface mounting package size of 600 um×300 um. The typical pitch on the passive LED tiles is in range of 3 mm to 10 mm.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object of the present invention to provide new and improved methods of dispersing semiconductor chips.
It is another object of the present invention to provide new and improved methods of dispersing semiconductor chips that preserves the neighboring relationship.
It is another object of the present invention to provide new and improved methods of dispersing LED chips into an array with preset geometric parameters while preserving the original chip order or neighboring relationship.
It is another object of the present invention to provide new and improved methods of dispersing multiple semiconductor chips at a given process time (i.e., parallel transfer process) that a LED display or light board can be made with fewer steps, more cost efficiently and time efficiently.
It is another object of the present invention to provide new and improved methods of making display/light board with higher chip counts, small pixel pitch onto single supporting substrates.
It is another object of the present invention to provide new and improved apparatus for dispersing semiconductor chips that preserves the neighboring relationship.
It is another object of the present invention to provide new and improved apparatus for dispersing LED chips into an array with preset geometric parameters while preserving the original chip order or neighboring relationship.
It is another object of the present invention to provide a new type of display and light panels with large area/thickness ratio of which the emitting elements are made of small size LED chips and are dispersed over large area.